Crystalline silica is a basic component of soil, sand, granite, and many other minerals. When reduced to respirable size particles, however, crystalline silica (including quartz, tridymite, and crystobalite) is a known human lung carcinogen and the mineral responsible for the lung disease silicosis. Respirable silica exposure is a serious concern for workers in industries that use silica sand and other silica-containing materials in their processing operations. For example, in the oil and gas industry, most new oil and gas wells are hydraulically fractured to stimulate well production. In these operations, silica sand is often used in combination with a fracturing fluid and large amounts of silica sand continually being filled and unloaded during these operations.
Certain vehicles that are used to move and transfer silica sand (i.e., sand movers, also called sand hogs, sand chiefs and sand masters) are not designed with occupational health considerations in mind; that is the machines are not configured with any means or mechanisms for containing, preventing or controlling the release of respirable size particles of silica and, as a result, significant quantities of respirable silica are released into workplace atmospheres, presenting a significant occupational health hazard for workers. Although personal respiratory protection (air-purifying respirators) are generally worn by workers, respirable dust containing crystalline silica is present in concentrations in the immediate vicinity of the sand movers that regularly exceeds the maximum use concentration for half-mask and sometimes for full-face air purifying respirators. Accordingly, there is a need to control primary emission sources to reduce the amount of respirable dust containing crystalline silica released during hydraulic fracturing and other similar operations that require moving large amounts of silica sand or other materials capable of generating and releasing potentially harmful particulates.